I have JFrame with 3 JPanel(basically three tabs). one of the panel has a textbox. there is value restriction on textbox. it means, user can enter only 1-1000 number in it. If he enters number >1000, it throws the warning message.
Now I am using focuslistener to save the entered number as soon as it looses the focus. But if the user enters 1200 and click on another tab(panel), it gives me expected warning message but also goes to the another tab. I need to remain in same panel if there is warning box. I don't want to loose the focus from the current panel.
mMaxLabelLength = new JTextField();
mMaxLabelLength.addActionListener(this);
public void focusGained(FocusEvent fe)
{
// do NOTHING
}
#Override
public void focusLost(FocusEvent fe)
{
saveActions();
}
public void actionPerformed(ActionEvent e)
{
//Do something
}
private void saveActions()
{
// error message
JOptionPane.showMessageDialog(this,
"Please enter an integer value between 1 and 1000.",
"Invalid Entry", JOptionPane.INFORMATION_MESSAGE);
SwiftApplication APP = SwiftApplication.getInstance();
int nMaxLabel = APP.getMaxPieLabel();
mMaxLabelLength.setText(new Integer(nMaxLabel).toString());
mMaxLabelLength.requestFocus();
}
The code block in the question does not offer too many details, but as far as I understand it, you need to use a VetoableChangeListener to prohibit focus change.
Here an example from Java2s:
import java.awt.Component;
import java.awt.KeyboardFocusManager;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyVetoException;
import java.beans.VetoableChangeListener;
public class Main {
public static void main(String[] argv) {
KeyboardFocusManager.getCurrentKeyboardFocusManager().addVetoableChangeListener(
new FocusVetoableChangeListener());
}
}
class FocusVetoableChangeListener implements VetoableChangeListener {
public void vetoableChange(PropertyChangeEvent evt) throws PropertyVetoException {
Component oldComp = (Component) evt.getOldValue();
Component newComp = (Component) evt.getNewValue();
if ("focusOwner".equals(evt.getPropertyName())) {
if (oldComp == null) {
System.out.println(newComp.getName());
} else {
System.out.println(oldComp.getName());
}
} else if ("focusedWindow".equals(evt.getPropertyName())) {
if (oldComp == null) {
System.out.println(newComp.getName());
} else {
System.out.println(oldComp.getName());
}
}
boolean vetoFocusChange = false;
if (vetoFocusChange) {
throw new PropertyVetoException("message", evt);
}
}
}
But, the more I think about it, maybe using InputVerifier and public boolean shouldYieldFocus(JComponent input) is more appropriate. See "Validating Input" in the "How to Use the Focus Subsystem" of the Java Tutorial.
Looks like you are looking for an InputVerifier.
Abstract class that allows input validation via the focus mechanism. When an attempt is made to shift the focus from a component containing an input verifier, the focus is not relinquished until the verifier is satisfied.
As the oracle page describes, it can be used to write own verifiers, which reject invalid inputs and keeps the focus meanwhile on the associated JComponent.
Therefore you just need to do two things:
Write your own InputVerifier, e.g. MyVerifier or take one of the already existing ones and create an instance of it. (See below for a small complete verifiable example)
Register your verifier instance on the target JComponent using calls to the Input Verification API.
This means, to register an...
InputVerifier call the setInputVerifier method of the JComponent class. For example, the InputVerificationDemo has the following code:
private MyVerifier verifier = new MyVerifier();
...
amountField.setInputVerifier(verifier);
Note For some reason I can't find a source for the java8 InputVerifier right now, it seems that the link is broken.
Small Verifiable Complete Example (from here)
import java.awt.*;
import java.util.*;
import java.awt.event.*;
import javax.swing.*;
// This program demonstrates the use of the Swing InputVerifier class.
// It creates two text fields; the first of the text fields expects the
// string "pass" as input, and will allow focus to advance out of it
// only after that string is typed in by the user.
public class VerifierTest extends JFrame {
public VerifierTest() {
JTextField tf1 = new JTextField ("Type \"pass\" here");
getContentPane().add (tf1, BorderLayout.NORTH);
tf1.setInputVerifier(new PassVerifier());
JTextField tf2 = new JTextField ("TextField2");
getContentPane().add (tf2, BorderLayout.SOUTH);
WindowListener l = new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
};
addWindowListener(l);
}
class PassVerifier extends InputVerifier {
public boolean verify(JComponent input) {
JTextField tf = (JTextField) input;
return "pass".equals(tf.getText());
}
}
public static void main(String[] args) {
Frame f = new VerifierTest();
f.pack();
f.setVisible(true);
}
}
Related
I've encountered a problem while trying to call a method within a class that implements actionListener. The method being called, DataCompiler, needs to use the integer wordCountWhole, which is returned in the wordCount class. The problem is that I can't pass the required parameter to the actionListener method.
import javax.swing.*;
import java.awt.*;
import java.awt.List;
import java.awt.event.*;
import java.beans.PropertyChangeListener;
import java.text.BreakIterator;
import java.util.*;
import java.util.stream.IntStream;
public class GUI extends JFrame {
public JTextArea textInput;
public JButton dataButton;
public String str;
public GUI() {
super("Text Miner");
pack();
setLayout(null);
dataButton = new JButton("View Data"); //Button to take user to data table
dataButton.setSize(new Dimension(120, 50));
dataButton.setLocation(5, 5);
Handler event = new Handler(); //Adds an action listener to each button
dataButton.addActionListener(event);
add(dataButton);
public class wordCount {
public int miner() {
//This returns an integer called wordCountWhole
}
}
public class Handler implements Action { //All the possible actions for when an action is observed
public void action(ActionEvent event, int wordCountWhole) {
if (event.getSource() == graphButton) {
Graphs g = new Graphs();
g.Graphs();
} else if (event.getSource() == dataButton) {
DataCompiler dc = new DataCompiler();
dc.Data(wordCountWhole);
} else if (event.getSource() == enterButton) {
wordCount wc = new wordCount();
sentenceCount sc = new sentenceCount();
wc.miner();
sc.miner();
}
}
}
}
And here's the code for the DataCompiler class:
public class DataCompiler{
public void Data(int wordCountWhole){
int m = wordCountWhole;
System.out.println(m);
}
}
You don't add the parameter there because you've invalidated the contract of the interface.
Use a constructor* (see note below, first)
public class Handler implements Action{ //All the possible actions for when an action is observed
private int wordCountWhole;
public Handler(int number) { this.wordCountWhole = number; }
#Override
public void actionPerformed(ActionEvent event) {
Although, it isn't entirely clear why you need that number. Your DataCompiler.Data method just prints the number passed into it, and that variable seemingly comes from nowhere in your code because it is not passed to the ActionListener.
* You should instead use Integer.parseInt(textInput.getText().trim()) inside Handler class / the listener code and not use a constructor. Otherwise, you'd always get the number value when you add the Handler, which would be an empty string and throw an error because the text area has no number in it.
Additionally, wc.miner(); returns a value, but calling it on its own without assigning it to a number just throws away that return value.
I'm going off of what I saw in a textbook to make an action listener for a button. To do it, I made an inner class. When I try to call the inner class, the error comes up: cannot find symbol.
Here's the code:
package GUI;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ATMGUI extends GUI
{
public ATMGUI()
{
this.makePane();
this.makeButton("Withdraw");
button.addActionListener(new WithdrawListener());
pane.add(button);
this.makeText("Enter amount to withdraw: ");
pane.add(text);
this.makeTextField("Enter amount here");
pane.add(field);
this.makeFrame();
frame.add(pane);
class WithdrawListener implements ActionListener
{
public void actionPerformed(ActionEvent click)
{
System.out.println("This is a test.");
}
}
}
//------------------------------------------------------------------
public void makeFrame()
{
frame = new JFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
frame.setVisible(true);
}
public void makePane()
{
pane = new JPanel();
pane.setLayout(new GridLayout(3,3));
pane.setVisible(true);
}
public void makeButton(String buttonName)
{
button = new JButton(buttonName);
}
public void makeText(String addText)
{
text = new JLabel(addText);
}
public void makeTextField(String addText)
{
field = new JTextField(addText);
}
}
This is the particular bit that is giving me trouble
button.addActionListener(new WithdrawListener());
I saw somewhere else that it had to be instantiated in a certain way.
I tried something like:
ATMGUI a = new ATMGUI();
ATMGUI.WithdrawListener w = a.new WithdrawListener();
and then put w in for the argument, but that didn't really work for me either.
Not sure if it is because I'm working in a subclass. Also not really sure if things need to be done differently because I'm working with an interface.
Place the WithdrawListener outside of the constructor context
public class ATMGUI extends GUI {
public ATMGUI() {
//...
button.addActionListener(new WithdrawListener());
//...
}
class WithdrawListener implements ActionListener {
public void actionPerformed(ActionEvent click) {
System.out.println("This is a test.");
}
}
Add listener to button after local class declaration.
public void abc(){
PQR pqr = new PQR(); // incorrect
class PQR {
}
}
Correct way is
public void abc(){
class PQR {
}
PQR pqr = new PQR(); //correct
}
It seems like you must declare the local class before you use it. The follwing code snippets I tested:
This one showed no errors:
public void testFunc() {
class Test {
}
Test test = new Test();
}
But this one does:
public void testFunc() {
Test test = new Test();
class Test {
}
}
Edit: Sorry for posting nearly at the same time, next time I will check three times if someone already posted.
Use of anonymous type is recommended when you are not reusing a class.
Have a look at it (frequently used with listeners) - It's a great answer!!
quoted from above link
Using this method makes coding a little bit quicker, as I don't need
to make an extra class that implements ActionListener -- I can just
instantiate an anonymous inner class without actually making a
separate class.
I only use this technique for "quick and dirty" tasks where making an
entire class feels unnecessary. Having multiple anonymous inner
classes that do exactly the same thing should be refactored to an
actual class, be it an inner class or a separate class.
this.makePane();
this.makeButton("Withdraw");
button.addActionListener(new ActionListener() { //starts here
public void actionPerformed(ActionEvent click)
{
System.out.println("This is a test.");
}
});//ends
pane.add(button);
this.makeText("Enter amount to withdraw: ");
pane.add(text);
this.makeTextField("Enter amount here");
pane.add(field);
this.makeFrame();
frame.add(pane);
I have an error for the code below. Sorry if this is too basic as I am new to java.
Basically, I cannot retrieve the String "44418" from the class CityChange.
I know the reason is because I created a new instance cc in the class MainPanel.
However I do not know any other way of doing it.
public class CityChange extends JPanel {
public CityChange() {
JButton btn1 = new JButton("London")
this.add(btn1);
btn1.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent evt) {
//London Yahoo Weather Code 44418
setCitySelected("44418");
}
});
}
public void setCitySelected(String citySelected) {
this.citySelected = citySelected;
}
public String getCitySelected() {
return citySelected;
}
private String citySelected;
}
public class MainPanel extends JPanel {
public MainPanel() {
CityChange cc = new CityChange();
System.out.println(cc.getCitySelected()); //returns null instead of 44418
}
}
Please give some advice. Thank you.
For timing reasons, the value has no choice but to be null.
What happens here "immediately" (at init time) is that a new CityChange object is created and its citySelected is gotten and printed. As nobody set it otherwise, it is null.
Only after firing the event (clicking the button), it gets a value, and if you print the value then, you'll see the new value.
The code setCitySelected("44418"); is only executed when you call the method public void actionPerformed(ActionEvent evt) which is not happening at the moment. This Method is only called via a Button in a GUI so you first need at least a simple Window with a Button. Here is a good example http://docs.oracle.com/javase/tutorial/uiswing/events/actionlistener.html
I am trying to make a web browser for the fun of it, i seem to get errors when ever i put in my loadHtml method, when i comment that out everything works even the action listener.
import java.awt.*;
import javax.swing.*;
import java.util.*;
import java.awt.event.*;
import java.applet.*;
public class browserPannel extends JFrame{
public static void main(String[] arg) {
JFrame browser = new JFrame("A Nun In A Weelchair");
browser.setSize(1000,700);
browser.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
browser.setLocationRelativeTo(null);
JPanel header = new JPanel();
header.setBackground(Color.lightGray);
JTextField url = new JTextField(20);
url.addActionListener(
new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
//loadHtml(event.getActionCommand);
System.out.println("action performed");
}
}
);
url.setSize(890,30);
url.setVisible(true);
JButton send = new JButton("Send");
send.setSize(75,30);
send.setVisible(true);
JEditorPane htmlc = new JEditorPane();
htmlc.setBackground(Color.red);
htmlc.setEditable(true);
htmlc.setContentType("text/html");
header.add(url, BorderLayout.SOUTH);
header.add(send);
browser.getContentPane().add(header, BorderLayout.NORTH);
browser.getContentPane().add(new JScrollPane(htmlc));
browser.pack();
browser.setVisible(true);
}
private void loadHtml(String link)
{
try{
//htmlc.setPage(link);
//url.setText(link);
}catch(Exception e){
System.out.println("ops sorry could not fined Virgine Mobile");
}
}
}
from what i can tell it looks like it can not recognize the url and the htmlc
I have tried to comment the htmlc.setPage and the url.setText, and when i do that my program compiles.
why am i getting these errors, shouldn't it recognize that they are defined above?
Your method isn't static but you're trying to call it from a static context (main()) Also, your instances in the main() method aren't visible in the loadHtml() method. You could pass them into the method (or declare them as static fields in your class). Finally, you shouldn't swallow Exception (at least printStackTrace()). So I think you were looking for something like,
private static void loadHtml(JEditorPane htmlc, JTextField url, String link) {
try{
htmlc.setPage(link);
url.setText(link);
}catch(Exception e){
System.out.println("ops sorry could not find Virgin Mobile");
e.printStackTrace();
}
}
Also, loadHtml(event.getActionCommand); isn't correct. You'd need parenthesis to call your original method loadHtml(event.getActionCommand());, but with the above changes it would be loadHtml(htmlc, url, event.getActionCommand()); (and to use the htmlc and url references in your inner class you must declare those references as final. For example, final JTextField url = new JTextField(20);).
Alternatively, you could make the components static so they're shared across all instances (and methods - first comment them out in your main method) -
private static final JTextField url = new JTextField(20);
private static final JEditorPane htmlc = new JEditorPane();
private static void loadHtml(String link) {
try{
htmlc.setPage(link);
url.setText(link);
}catch(Exception e){
System.out.println("ops sorry could not find Virgin Mobile");
e.printStackTrace();
}
}
Then you should be able to use loadHtml(event.getActionCommand())
I'm building a basic Point of Sale application and I've been looking for ways of having my main POS JFrame listen for bar code input. I found this code (slightly modified) posted by Cyrusmith, which looks like what I want but I don't know how to implement it in my JFrame. It looks like its intended to be a separate class, which is how I have it in my project currently. I asked my coworker and he doesn't know either.
Thanks for your help.
package barcode;
import java.awt.KeyEventDispatcher;
import java.awt.KeyboardFocusManager;
import java.awt.event.KeyEvent;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;
/**
* Listens for bar code input and puts it into a String Buffer.
*
*/
public class BarcodeReader {
private static final long THRESHOLD = 100;
private static final int MIN_BARCODE_LENGTH = 8;
public interface BarcodeListener {
void onBarcodeRead(String barcode);
}
private final StringBuffer barcode = new StringBuffer();
private final List<BarcodeListener> listeners = new CopyOnWriteArrayList<>();
private long lastEventTimeStamp = 0L;
public BarcodeReader() {
KeyboardFocusManager.getCurrentKeyboardFocusManager().addKeyEventDispatcher(new KeyEventDispatcher() {
#Override
public boolean dispatchKeyEvent(KeyEvent e) {
try {
if (e.getID() != KeyEvent.KEY_RELEASED) {
return false;
}
if (e.getWhen() - lastEventTimeStamp > THRESHOLD) {
barcode.delete(0, barcode.length());
}
lastEventTimeStamp = e.getWhen();
if (e.getKeyCode() == KeyEvent.VK_ENTER) {
if (barcode.length() >= MIN_BARCODE_LENGTH) {
fireBarcode(barcode.toString());
}
barcode.delete(0, barcode.length());
} else {
barcode.append(e.getKeyChar());
}
return false;
} catch (UnsupportedOperationException err) {
throw new UnsupportedOperationException(err); //To change body of generated methods, choose Tools | Templates.
}
}
});
}
protected void fireBarcode(String barcode) {
for (BarcodeListener listener : listeners) {
listener.onBarcodeRead(barcode);
}
}
public void addBarcodeListener(BarcodeListener listener) {
listeners.add(listener);
}
public void removeBarcodeListener(BarcodeListener listener) {
listeners.remove(listener);
}
}
Most bar code readers basically inject the codes directly into the keyboard buffer. So if you had a JTextField which had keyboard focus, the resulting text would be "entered" directly into it...no magic involved.
If you "want" to use this reader, then you will need to create an instance...
BarcodeReader reader = new BarcodeReader();
Register a BarcodeListener to it...
reader.addBarcodeListener(new BarcodeListener() {
public void onBarcodeRead(String barcode) {
// Respond to the event, like, I don't know,
// set the text of text field :P
}
});
But to me, this just seems like a lot of extra work - but that's just me...
So, yes, it's suppose to be a separate class. Depending on what you want to achieve, you could dump somewhere in your current code base, import the class into your source code and use it like any other. Equally, you could create a separate library for it, but this just means you need to include it within the classpath for compiling and runtime execution as well...